


Seek The Because

by Grassy



Category: Ao no Exorcist | Blue Exorcist
Genre: Canon - Anime, Community: smallfandombang, Drama, F/M, Genderswap, Sexual Content, Spoilers, Twincest
Language: English
Status: Completed
Published: 2012-05-26
Updated: 2012-05-26
Packaged: 2017-11-06 01:09:41
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 10,585
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/413051
Author URL: https://archiveofourown.org/users/Grassy/pseuds/Grassy
Summary: <blockquote class="userstuff">
              <p>Yukio belonged to Rin; Rin belonged to Yukio.  That was always how things would turn out in the end.  Sealed powers or no, they were neither one precisely human.  Maybe it was instinct, maybe it was history, maybe they were just that screwed up.  Whatever the reason, it was love.</p>
            </blockquote>





	Seek The Because

**Author's Note:**

> *blushes* I am- _so embarrassed_ by how much effort was put into writing the porn in comparison to pretty much everything else. But it makes sense, I guess. Originally I was just trying to write a smutty li’l piece for the kink meme with Yukio/girl!Rin tailplay - I didn’t expect it to spawn into something so- Gah! Genderswap love, why must you do this to me~ (TT^TT) On the other hand, this is the longest thing I have ever posted. Not that I’ve written - I mean, I’ve got stuff on my computer - but nothing else is in any fit state to be viewed by others. I am so proud of me~♥
> 
> Also, check out the art for this done by the amazing seraphcelene [here~](http://seraphcelene.livejournal.com/244167.html)

“Do not seek the because - in love there is no because, no reason, no explanation, no solutions.”  
Anaïs Nin

  


**prologue: line up, piece by piece**

  


Under other circumstances, Shirou woudn’t have taken in either child, especially as one was a girl. But circumstances weren’t anything resembling normal, the men of his church knew that, and Shirou didn’t trust anyone else to raise them properly.

Had Shirou only handled Yuri’s situation differently, maybe the outcome would have been changed for the better. So he had a debt that needed to be paid; to Yuri and the babies she had given everything to bring into the world as well as to everyone who had died on that Blue Night when Satan had destroyed so many good people in search of a host to save his lover and the lives they had created. Not to mention the bet he had made with Mephisto that he had absolutely no intention of losing.

  


Take them in, raise them as humans. Shirou had said those very words to Mephisto, so long ago. So many, many…

Had it only been three weeks? Seriously?

Shirou was going to _die_ at this rate. Possibly from lack of sleep and nicotine withdrawals; the ensuing insanity requiring the other men to put him down like a rabid dog. Or from some no-name demon passing him by and not realizing, in his exhaustion, until after said demon made off with Shirou’s _head_. (Only, yeah, more likely the former than the latter. Even wanting to keel over and play dead until he’d recovered from his new role as caretaker to constantly-needy twins, Fujimoto Shirou was fucking badass. No way he’d ever go out at the hands of such a lame enemy. His own men… At least they’d come up with something cool to tell people.)

Whoever said parenting was easy in comparison to being an Exorcist on active duty deserved to be strung up and tortured brutally. Then forced to take in a score of young orphans to raise. _Without help._

The only saving grace was that everything Rin and Yukio did, they did pretty much in unison; eat, cry, vomit, fill their diapers. But that also meant they _slept_ on the same schedule. If not for that one, miraculous thing Shirou would have been done for within days.

Though he dreaded the day that he’d be forced to start them sleeping in separate beds and, eventually most likely, separate rooms. Even as infants they were clingy but he’d heard things from exorcists whose families had more demonic heritage than most. One had to be careful of the attachments between their children, lest siblings become closer than generally approved of. Especially twins that might already gravitate toward one another. (Yeah, Shirou wasn’t going to forget anytime soon the things Mephisto had been talking around in such a way as to drive Shirou _crazy_ , in regard to the effects of demonic blood in opposite-gender twins.)

But until such a time (still months, _years_ away) came, he’d enjoy the moments - few and far between though they were - when Rin and Yukio slept peacefully in their crib. He’d always been able to fall asleep anywhere and anytime, but catnaps were fast becoming his true specialty.

  


* * *

  


**part one - separate, combined strength**

  


Terrified adults and children watched as the priest moved closer to the small, raging figure that stood in the middle of broken furniture and toys. Stern, disapproving words did not seem nearly enough in response to the chaos she had unleashed.

But Shirou knew his daughter better than any save her brother, though he could take no chances in hoping the boy could calm his sister. Rin would never forgive herself if she harmed Yukio.

And Shiro was certain he knew the reason for such a vicious outburst the moment he had caught sight of her.

The shoulder-length twin tails Rin had so proudly left home with that morning had been shorn; drooping, uneven stubs gathered together with loosening white ribbons all that remained. Long clumps of inky blue-black hair strewn across the floor alongside child-sized scissors spoke volumes.

“They said- they said I’m a monster! And- and I should _look_ like one!” Rin wept openly, sorry and angry and sad and _make it better, **please**_. Because if anyone could fix things, it would be Otou-san.

Shirou drew his daughter into his arms, ignoring how she lashed out at him in her fit of upset. Ignoring the pain of, yes, definitely broken ribs as he clutched her against him. To pull away from her now… Rin was so fragile in ways many didn’t realize between their misconceptions and Rin’s attitude. But he loved her so much and when she realized the extent of what she had done, Rin would be hurting much worse than he did.

So he kept holding on until the paramedics forced him to let his girl go.

  


* * *

  


Yukio was a crybaby. That was just a fact in Rin’s world. But for him to cry because of other people hurting him; because of stupid bullies who should know better than to touch what belonged to Okumura Rin-

That was unacceptable. And she’d show them just what the punishment was for doing such a thing.

(Some part of her, distant and cold, did not understand what was happening. Her usual rages were furious, unthinking; often due to direct insult toward herself. But this was an attack on _what was hers_. Not the same thing at all; the usual flood of shame at harming others didn’t apply.)

In the aftermath, leaving weeping boys and scared girls in her wake, Rin strode away proudly. Yukio’s small hand in her own, they left the playground quickly. When they were closer to home, Rin turned to her younger brother and smiled.

“It’s okay, Yukio. I won’t let them hurt you anymore. And! There’s a spell I wanna try. Just for you.”

“A magic spell? For me?” Wide turquoise eyes stared at Rin in wonder.

“Un.” Hands on her hips, Rin grinned brashly at her twin. “A charm, to cheer you up!”

Yukio hiccupped, rubbing the tears from his dirt-smeared face. _If other weird and scary things exist…I guess good magic can, too. Nee-san does stuff like that? Is she a magical girl?_

“O-okay. If you think it’ll work.”

“Trust Onee-sama! Now c’mere.”

Rin pushed Yukio onto a nearby bench, flopping down next to him; maneuvering them about and wrapping her hands around his own as they faced one another. With a determined mien, she slowly and gently pressed one, two, three kisses upon his face; beneath his left eye and upon the side of his chin.

_My moles… What?_

Frowning, Rin repeated the actions a second time. Then a third. She tried for a fourth when Yukio finally pulled away with a laugh.

“Nee-san, stop it! That tickles.” Pink with embarrassment, Yukio rubbed his nose with the back of one hand.

“There.” Rin smiled, wide and bright, her eyes closed in pleasure. “Next time you’re sad, I’ll do it again until you’re happy.”

Snuggling into his sister’s arms, Yukio sniffled a bit. No matter what anyone said, Nee-san was the best person in the whole world. Someday, he’d be strong and protect her, too. Until then…

“Thank you, Nee-san.”

  


* * *

  


Once Yukio began training to become an exorcist he no longer cried in front of his elder sister. Rin was obviously hurt by his sudden distance, but didn’t let it get her down overmuch. And Yukio let her cuddle him like a plush toy in return for the independence.

“Yukio’s gonna be a man at some point, I guess,” Rin had muttered when Shirou asked her about it, face contemplative and distant. “But if he’s becoming the Knight, does that mean I’m the Princess now instead of him? How would that even work…”

That, Shirou thought, was probably the moment he was forced to admit his kids were seriously warped in their own ways. Not that he’d ever really doubted such, he _knew them_ after all, but a man hoped when it came to certain things. Although…

In addition to her ever-improving culinary skills, Rin had finally begun to grow her hair out once again. Even with her temper and strength, she would certainly make a very pretty princess. Or a truly unique bride for the right man someday in the future. If she would ever agree to such a thing.

Or if Yukio would ever allow it.

(Shirou had his doubts about either option.)

  


* * *

  


It wasn’t that Yukio didn’t love his sister. He did. But he had secrets to keep from her; things he had to learn to some day protect her the way Tou-san always had. Especially if the worst came to pass and Tou-san was- If Tou-san was ever unable to protect Nee-san anymore.

And Yukio had never objected to Nee-san crawling into bed next to him on nights she felt that increasing distance between them. Only…such had become awkward as it never had before.

Yukio was called a genius for good reason, he knew what was happening to his body. Knew why the sight of Nee-san sprawled out next to him - sleep-shorts baring long legs and shirt riding up to expose her soft belly - left him squirming and flushed and a bit fuzzy in the head. Knew why he woke up cuddled against her, pressing closer and closer into her for contact. Knew why he continued to allow her to kiss him on the lips, returning the favor each time with fervor.

He also knew why Nee-san kept her thighs pressed together sometimes, a line of pink across her nose as she tried to get as close to him as possible without actually moving at all. Knew why she turned away on occasion, arms across her breasts to keep them hidden from view. Knew why she shivered, but didn’t pull away, when he held her close, legs tangled together and his hands hot on her skin wherever he touched.

He knew what all of those things meant and he knew that they were wrong. He just didn’t care.

(Yukio’s feelings for his twin were one of few truly real and right things in his world; something he had never doubted. And for all the distance that had come between them, he knew Rin felt the same way. No one would take that away from them.

No one.)

  


* * *

  


“Seriously, you need to drink more milk, Pettanko-chan, if you want to grow up into a boobylicious babe.” Shirou avoided the angry swipes of Rin’s spatula with ease; smirked just to piss her off that much more.

“Wha-” Rin squawked, puffed up like an angry kitten. Her chest was _not that flat_. If it were, why the hell would they have to shell out so much for comfortable undergarments? “Shut up!”

“Just saying, Rinrin.” That baking sheet would have been perfect for a shield, but Rin trusted him not at all with the contents of her domain. He’d likely take it to the face and _then_ be forced to pay for a replacement. Not cool.

“Bastard, just who’s ‘Pettanko-chan’?! I’m thirteen, you perverted old man, it’d be _weird_ if I had huge tits. _Especially_ when I’m still gaining in height,” Rin snarled at him as she emphasized her words with the cooking chopsticks added to her repertoire of kitchenware weaponry.

Shirou winced as Rin managed to pinch a bit of skin here and there while she defended herself with the spatula. Rin was definitely a talented fighter. True, he’d wipe the floor with her in moments if they were going at it seriously, but even so. To catch him while rough-housing was still quite the accomplishment. (He didn’t count the injuries brought about by her rages growing up, that was a different matter altogether.)

“Otou-san, could you please stop winding up Nee-san?” Yukio’s cool voice interrupted their childish display. One long finger pushed dark-framed glasses further up the bridge of his nose, obviously not impressed.

“Uwah, Yukio!” Shirou smiled brightly at his son, ignoring the storm clouds gathered above the boy’s head. Kid really needed to lighten up more often. “You’re totally rocking the scary, shiny glasses look.”

Yukio twitched, disarming Rin in an easy movement and holding her close to keep either of them from lashing out at their father. “Aren’t you supposed to be resting? Like the doctor recommended?”

“It’s just a sprain, I’ll be fine.” But he got the message. Between Shirou’s own juvenile behavior and Yukio’s overbearing fuss, Rin had finally lost the worried edge she’d had since he and Yukio returned from their latest mission. (Though she still clung determinedly to Yukio’s arm, worryingly obvious with how the two regulated physical contact in front of others, especially their father. Shirou tried not to think on that too hard.)

Thankfully, Rin had no clue how close a call it had actually been or neither Shirou nor Yukio would ever again be allowed to leave the church without her say-so; a hassle they couldn’t afford, considering.

They’d both have to be more cautious in the future, lest Rin start demanding answers they hoped to never have to give her. Or worse, have her stumble into trouble while trying to find out for herself.

  


* * *

  


Rin stared at the slouched figure haloed by the dim lamplight, her brow furrowed speculatively. Closing the door softly behind her, Rin padded over to slide onto Yukio’s lap wordlessly.

On instinct born from experience, Yukio braced Rin’s hips as she straddled him. The ominous creaking of his desk chair - needed to be replaced, sooner rather than later - was ignored in favor of the warm weight pressed against him.

“Nee-san, what in the-”

“Lose the gloomy face, unless you want me to start asking _why_ you’re being all emo.”

Sharp eyes narrowed, angered by her presumptuousness.

“That’s better, but…”

The soft press of lips to his face - one, two, three - froze the biting response in Yukio’s throat. That was- It had been so long, he’d nearly forgotten. Nee-san’s magic spell, just for him.

“…cheer-up charm.”

“So you do remember. Wasn’t sure whether you did or not.” Rin’s lips twisted into something not quite a smile. “You haven’t seemed to need it like you used to.”

Yukio, lost in memory, pulled Rin closer to rest his forehead upon her shoulder. His eyes closed as blunt nails carded through short hair, a pleasant skritch over his scalp. Just as easily as she wound him up, Nee-san knew how to calm him down.

“Sorry, but- Could you not ask? And just let me stay this way for a while?” If he didn’t acknowledge the quaver in his voice, maybe she wouldn’t, either.

“…sure.” The way Yukio had been acting worried Rin, but confrontations or whatever could come later. She was just happy to be relied upon again; Yukio had gotten so independent as they grew up. It was natural, but still. Rin missed being the one to protect him from the world outside of just the two of them. But… These moments, she knew he was still _hers_. No matter how distant he could be at times.

That was enough for now.

  


* * *

  


Yukio was quiet, for once not off on a lecture about Rin having gotten into yet another fight as he patched up her wounds. He was quite proud of himself for that. Yukio wanted to rage, to scream; wanted to shake his elder sister with hands very determinedly _not trembling_ over her recklessness. Instead, he continued to clean the blood and tears from her scuffed face.

Her…unique nature…notwithstanding, Rin had been ganged up on by several punks she’d had prior altercations with. Not even Nee-san could go without feeling the results of two particular brutes’ manhandling of her so as to violently introduce Rin’s face to a _brick wall_.

That carelessness, that inability to keep herself out of danger was what Yukio took issue with. (It was.) Really. (Partially.)

It wasn’t as though Yukio had any desire whatsoever to find those bastards and introduce _them_ to some of the skills his father and Shura-san had taught him over the years. Couldn’t be that at all. (Because if it had been, if Yukio were to let himself start then he would _never stop_. Such filth, human or not, were in no way important enough for Yukio to resort to such extreme methods. After all, if Nee-san with her temper and strength could avoid having dealt such fatal damage then Yukio could do no less himself.

That did not mean he wouldn’t try to find another solution.)

“Thangs fer helbing me oud, Yugio.” Rin licked a bit of blood from the side of her mouth.

“Don’t talk, Nee-san. It can be hard enough to decipher your words normally, I don’t want to try while I’m distracted.”

“Ogay.” But Rin’s eyes were soft, apologetic. She didn’t enjoy scaring him in such a way, despite having done so countless times over the years. So she stayed quiet and let Yukio reassure himself that she was alright.

  


* * *

  


**part two - the world, of perspective**

  


Rin had thought Yukio leaving to move into the school dormitory he would be living in and losing her new job on the first day because of some weird _thing_ would be the worst parts of her completely shitty-ass week.

There were no words for just how wrong she had been. Or for how much she wished that they were.

(Rin had grown up in a church, she knew who Satan was. And she knew fear that she had never known before. Those things, that world- She didn’t understand any of it anymore. Except…

_Ever since I was little I knew I wasn’t good._ )

So much of that desperate run back home before the sun set, hand in her father’s own tight grasp as he battled the demons chasing them, was a blur. But everything that wasn’t- It was all sharp, overly realistic in an unreal way.

(Why, why did it have to be real? Was that her punishment for having been born?)

Being led into that small space, the key that opened up something she never wanted. Kurikara in her hands as her world tumbled down around her.

Those words. How dare she speak those words. They condemned the father who loved and raised her, who had braided her hair and teased her about the size of her breasts.

_I truly am a demon._

  


Maybe the way he’d gone about everything had been wrong. Maybe he should have revealed the secrets of Rin’s birth to her long ago; with Yukio’s help she would have believed it, even. The past was the past, however, and there was no more time for regrets.

(Even though Shirou wished he had never slapped her to stop those words her pain and fear let loose. That was not a memory he wanted her to keep. Not a memory he wanted to have.)

But Shirou had raised the best damn kids in the world.

“At last I’ve got this body!”

And, much as he didn’t want to place the burden on their shoulders, it was their turn to do the rest.

“She’s my daughter! And you’ll give her back!”

  


She could feel it too well. The sword she had latched on to, to pull the both of them out of the gate. It was right there, in her hands. He’d told her not to, but-

(How often had she disobeyed his words before?)

Then the Gehenna Gate was gone. The sun rose on a new day. And her father was dead.

Rin clutched at the sword to stay upright on her knees. Her tears fell, but nothing would change.

“Tou-san…”

“Nee-san?”

  


* * *

  


“I’m sorry… I’m sorry… _I’m so sorry…_ ”

The bedcovers clenched around her to block the outside world from her senses, Rin sobbed helplessly into her tear-soaked pillow. For Tou-san. For Yukio. For herself.

Once upon a time, not so very long ago, Yukio would have been right there with her; beside Rin on the bed or under the covers himself if he could not coax her out from beneath them. But that was before Rin had been a demon, before she became the reason their father had to kill himself. Before Rin had destroyed everything.

(How could Yukio ever look at her again without secrets and lies and death hanging heavy between them?)

No matter how awesomely badass their father had been in those final moments, it was because of Rin that he’d been forced into such a position at all and _oh, God, my daddy is gone…_

Her father’s cell phone sat abandoned on the floor beside her bed. She’d have to make that call soon enough, but for now-

All she could manage at the moment was to cry.

  


* * *

  


The lonely figure that had stood, heartbroken and rain-soaked with the Koumaken sheathed upon her back, before the stone bearing the late Fujimoto Shirou’s name could not possibly be his sister.

Yukio did not wish to believe it was Nee-san. His beautiful, beloved twin sister. Not that- that _demon_.

She looked and sounded so much like Nee-san (touch and taste and scent and-) but, _no_. The demon was not, could not be, the sister Yukio had decided to protect with everything he was and would be all those years ago. But…she _was_.

Much as he wanted to reject the possibility of such a thing ever being truth, Yukio knew better. Satan’s blue flames, the demonic powers sealed away into that sword just after their birth; that was proof undeniable of who she was.

They had been unable to prevent Nee-san from awakening as a demon, despite all the preparations that had been made and other sundry measures they had taken over the years.

And that failure - of his own, of Tou-san’s, even of Rin’s - was so much harder to accept than anything else.

  


But even so. _Even so._ Nee-san was his twin, his reason, his _everything_. It hurt to hate her. So Yukio pretended. Fake smiles and calculated indifference, all to cover what he wanted to hide.

(That made it even harder. So close, yet so far, and only Rin’s own grief had kept her at a distance.)

Then Nee-san was screaming at him, infuriated as she so rarely was with Yukio, and a shattered vial of blood finally destroyed his façade.

It was so much easier when he had something to do. And Yukio’s guns had yet to let him down.

“Anyway, what did you think about me until now?”

But the filth that spewed from his lips, from the darkest part of himself- Every word broke Rin’s heart.

“Are you saying it’s my fault that he died?”

“Isn’t it so?”

And his own.

“If Tou-san had any weakness it would have been you, Nee-san.”

Even- especially since it was truth.

(Though Nee-san had been right as well; Yukio had no right to aim a gun at his sister.)

  


Rin couldn’t remember ever having been so pissed off. Not without her wanting someone seriously dead. But for _Yukio_ of all people to…

“I didn’t kill our father.”

For all her fault in the mess that resulted in Fujimoto Shirou’s death, that was one truth Rin knew now. _She_ hadn’t killed Tou-san; _Satan_ had. Someday she would make him pay for it.

But.

“I don’t want anyone to die for me anymore!”

(And after all that drama, all the angst and blame and epic fight turned touching reunion scene-

“Are you surprised? I insisted and they put us in the same room. Also, we’re the only ones in this dorm.”

Yukio? Was _such_ a bastard. Plus, even if it was no longer used it was still a _boys’_ dormitory. What the hell?!)

  


* * *

  


It really had been too long since they’d last touched one another in such a manner - even before Rin’s powers were unsealed and their father died to protect her from Satan. They had been busy with all of the preparations for Yukio’s eventual departure to school and dorm life. (Rin had been so proud of him, but he’d still been _leaving her_ and she just- hadn’t known how to accept that separation so she had tried to be less clingy.)

After…well.

Neither had been in a mood for it then, not for comfort nor to simply reassure themselves that they still had one another. Rin had felt too guilty - it was _all her fault_ that their father was dead - without the slightest clue how to explain everything that had happened to Yukio. And for all that Yukio had _wanted_ her, he couldn’t bring himself to touch the demon that had been responsible for so much chaos and death, no matter how much he loved her.

Not until that horrible confrontation in the classroom, secrets and shame and anger finally bared to each other as demons were brought down one after another between their combined strengths. Even then, the aftermath of that had been one of reassurance; soft kisses and cuddles and snark, more familial than sexual. (It had also been the first real rest either had gotten in some time, sleep much more important at that time than sex.)

Things were different now, in her changed form. So much of Rin was still the same, enough so to be a danger with the parts of her that were no longer what they had been.

Physically, she’d always been the stronger one. Her tail had a mind of its own, but extreme sensitivity made avoidance a simple thing and her ears… Well, they were just a bit pointy and Rin had always enjoyed them being played with. It was her teeth - _fangs_ , fucking _seriously_ \- that seemed to cause no end of problems. Like, logistical issues and stuff. Especially during oral sex.

From the moment signs of puberty started kicking in Tou-san had been ultra-paranoid about putting her on birth control - which made a great deal of sense in hindsight, especially considering how regulated and difficult such things could be to access in Japan - and his many warnings (ravings) about horrible, perverted men of all ages and the dangers of doing things one is absolutely not ready for ( _until they’re twenty- no, thirty!_ ) had left Rin somewhat paranoid about giving it up. ( _That way_ at least. By the time she’d actually agreed to vaginal sex, Rin and Yukio had already tried so many other things that it was just- Well, amazing, it always was with them. But toys had broken her body in and while the real thing was multitudes better, in certain respects there wasn’t all that much difference.)

Rin had worked hard on her skills over the years - had pawed through the old man’s porn stash and poked about the internet for interesting tips and tricks to try out - especially in learning how to blow a guy. (Well…Yukio. No other men ever entered her range of vision in that sense.) It was something she enjoyed, both for the act itself and the control it gave her over Yukio; something she didn’t often have outside of sex-type stuff.

But the new teeth Rin sported after her powers had been unsealed were sharp and dangerous and _oh, shit,_ what if she damaged some rather important parts of Yukio’s anatomy?

So, horrible though Rin was at doing so, ultra-careful was the only way to go to keep from doing major harm to Yukio’s body.

  


Nails scraped over one flushed nipple while dexterous fingers twisted the other lightly. A hitched breath, soft pants betraying a determined silence.

“Na… Your tits are sensitive as ever, Yukio~” Rin’s slick tongue caught a bead of sweat that trailed down Yukio’s neck.

“Hng! Nee-san, would you please stop saying things like that?”

“Haha, yeah right. If you haven’t gotten me to stop after all this time, you really think I will now?”

Bare breasts pressed against the smooth skin of Yukio’s back, a distraction and temptation with what he could feel but not yet see from her kneeling position behind him on the bed.

Rin knew just how much Yukio loved her breasts - loved to touch and taste and let her fuck him with them - but that wasn’t the goal, not this time. Rin needed to feel him, to memorize her twin with the new senses she had that left her twitchy and restless and kept Rin from her usual eleven hours of sleep, fucking _hell_.

So she did, warm hands that skimmed over his bare chest down to the shiny belt he wore with his black dress pants. A teasing brush of fingers; his hands tightly clenched, obviously wanting to reach for her to- Stop her or maybe just touch her in return, Rin wasn’t sure. But he’d been good so far, she could treat him.

Rin slid the long length of leather from the buckle, then chose to ignore it in favor of other matters. (Sometime, definitely, she’d do something with that. Restrain his arms, maybe, or let him tie her legs together the way he did that left Rin _so tight_ when he slid deep inside her.)

The button slid free, zipper undone with a whisper of sound. Yukio forced himself to not stifle the noises of pleasure that escaped him. Where they were, pretty much alone in the building, neither had to keep on guard so as to not have what they were doing be discovered. (Anyone meant to be observing more than likely already knew what was between them.) And the last thing he needed to do now was encourage Nee-san to taunt him further in order to make him react.

She pressed a quick, nip of a kiss to the nape of Yukio’s neck before her hands slid into pants, beneath boxers to wrap around his cock. He was so hard, leaking as she drew him gently from his clothing.

“Nee- Nee-san, more. Don’t tease. Not now, don’t tease.” He flushed at the breathless plea in his voice.

Her slick tongue tasted the skin behind Yukio’s ear, down the line of his neck; Rin’s smile was hidden against the curve of his shoulder.

“Alright.” Rin withdrew her hands; paid no attention to his whine at the loss of her body touching him as she pulled away. “Take off the rest of your clothes, Yukio. Please?”

Yukio kicked them off quickly, fighting briefly with a stubborn sock that refused to let go. When he looked up, Rin was- _Oh, God…_

Soft lips stretched by the fingers of one hand she’d had wrapped around his cock as she licked them clean in long swipes of her tongue before exchanging them with the other set. Her breasts, bare and perfect as always before him, framed by the flyaway wisps of her dark hair as if in offering. Mindless, his hands moved to drag her on top of him, face buried between the soft mounds of her breasts.

Rin squeaked, startled by the sudden switch and awkward angles of her legs.

“Yukio, wait. Lemme just- Ah!”

Mouth pulled away with a slick _pop_ , Yukio smirked. “Just whose breasts are the sensitive ones?”

“Well, _fuck_.” With a squirm to get her legs positioned around him more comfortably, Rin grimaced. Her panties just had to start to ride up into her. “You go all dog with a chew toy on ’em, of course they’ll be like that. Now would you _stop_ ,” she dug her nails into his thighs as warning.

“Nee-san?” Lust exchanged for worry, Yukio pulled back to meet her eyes.

“It’s alright.” Rin kissed him, tongue a light flicker across his lips in reassurance. “You’re just being the tease you asked me not to be. Not fair at all, little brother.”

Strong hands pressed him against the pillows as Rin slid down to pepper Yukio’s chest and abdomen with kisses; a trail of marks from lips and teeth and tongue. In retaliation for the breast gnawing she ignored his cock and spread his legs further apart to see all of him.

“Mmm…” Yukio was so pretty spread out before her. _Tasty…_

“Nee-san…careful!”

Rin looked up from where she’d nipped at the sleekly-muscled lines of one bare thigh, wordless question in her eyes.

“Just-” Reason battled briefly against lust within him. “Your teeth are different now. A bit of caution would be advisable at this point, yes?”

“Oh, right; forgot again. Damn.” Rin frowned, eyes crossing as she tried to glare down at her fangs. “Well, this is a bummer. ’Cause I’m too worked up to figure this out right now. And it’s been so long, too,” she pouted. But no chances, not with such delicate bits.

Yukio let her slide back up his body; regretful himself, but willing to forgo the blow job one time around despite his desperation. With those untried fangs… _No._ Nee-san would undoubtedly give her all to figuring out the differences later, when they had the time and incentive. In the meantime, however…

“Oof. Pushy tonight, aren’t ya.” Rin smirked up at Yukio, cocksure as ever.

“I’m not letting you forget our current limitations in your hedonism. Or tease me by drawing this out because you can’t go down on me.” Grabbing his discarded pants, Yukio presented Rin with a packet of lubricant from one of the pockets.

Blue eyes lit up in understanding. “Like you don’t enjoy being teased sometimes, Yukio~” Sharp canines nipped at one strong, bare shoulder. “And no fair! You get your favorite but I gotta wait for mine.”

He kissed the petulant pout from her lips. “You’re such a cockslut, Nee-san.”

“Hey!”

“Just think of it,” Yukio slid soft cotton and lace down Rin’s legs; enjoyed the silky skin and strong muscles beneath his fingertips, “as something to look forward to. You can work out the handicaps on your technique while we figure out what new spell- and chemical-cocktail of contraceptives you’ll need.”

“And the paranoia about that makes so much sense, now…”

“Yes, even if you weren’t having dirty, sometimes outright kinky sex with your younger twin brother-”

“-the last thing I’d need was a kid. At my age or considering my heritage.” Rin rolled her eyes, despite the serious tone of her voice.

“Exactly.” Yukio couldn’t resist petting those lovely breasts once, twice more as Rin arched into his hands with a purr of pleasure.

“Still. You’re so making this up to me later.”

“Nee-san, you act as though you dislike this.”

“Oh, I like it. But it’s not fair that I can’t suck your cock but you still get to fuck my ass.” Rin’s tail flicked as if to announce her annoyance, but the way it tried to wind around Yukio’s forearm was telling in its own right.

As his hands ran over her body to roll Rin onto her stomach with familiar ease, Yukio supposed they made more sense in hindsight, all of Nee-san’s erogenous zones. The pleased whine that escaped when he nipped and nuzzled at her ears. How way she sank her teeth into- something, _anything_ when he ran hands, tongue, teeth down the smooth slide of her back to the soft swell of her ass and avoided direct contact with the base of her tail. (They’d been oh-so-careful back when living at the church, paranoid at being overheard and _still_ almost made too much noise the first time Yukio had touched that spot near the base of her spine. Without his mouth pressed to hers to muffle the short scream that had escaped- Well.)

Foil crinkled as he carefully tore open the packet, poured the lube over his fingers and between her cheeks. Knees spread and ass upturned as they were, Yukio could see just how wet she was. But desperate as he was himself, there was no time to play with her cunt as he might have been wont to do.

“Hah… _Yes_ , just like that.” Rin loved the feel of Yukio’s fingers as they slipped inside, stretched her loose with the ease of experience. It had been a while since he had fucked her ass, but the light ache from disuse was _just right_. Why the hell had they gone so long without, again?

Her needy whimpers and pants were muffled by the bedcovers. Yukio frowned, wanted to hear more. He’d not had nearly as much of her as he needed. Fingers removed with Rin’s resultant whine of displeasure and Yukio ran a hand down his cock to slick himself.

“Turn over. Now.” Yukio’s voice was low, lust and order in every word.

Without a sound of protest, Rin maneuvered herself around. Her hands slid down slick, shaking thighs to pull her knees toward her chest. Offered herself to Yukio with flushed face and blatant need.

“Good girl.” Eyes dark with intent, Yukio pressed the blunt head of his cock against her slick hole, slid in with one smooth, steady thrust.

“Nnn!” Rin released her legs, grasped Yukio with her thighs as nails clawed desperately at the bed. “Hah… Yukio!”

Eyes focused down at Rin as she moved, Yukio was somewhat glad that she couldn’t distract him this time by sucking his cock. Her needy whimpers and curses and the way her tongue flickered across her lips as she writhed beneath him, buried in the tight heat that surrounded him- Those were all things he missed out on when Nee-san went down on him.

“Nee-san… Nee-san… _Rin_ -”

Yukio knew Rin’s body, knew where to touch and taste to drive her wild. Despite the consideration they’d paid to her fangs for their potential destruction, both had simply ignored her tail due to its oversensitivity. But to remember anything when he was deep within her, ass clenched deliciously around his cock and her- her hands, fingers buried deep in herself, spread open and filling up and- It was instinct, to touch those parts of her body she enjoyed, especially that spot at the base of her spine-

Rin’s scream echoed in their room; tight, tight, _tight_ heat surrounded him and a curling, furred warmth pressed against his balls- stroked-

Yukio’s vision whited out.

  


Later, able to move and think again, Yukio was certain that Nee-san’s body had indeed become even more dangerous than before. Stamina was one thing, but that damned sneaky tail…

“Quite the mess we made, ne~” Rin grinned, fangs bare in her glee. Yukio was normally so starched and put-together that seeing him relaxed, sweaty-sticky, and smelling of sex - totally messed up by her, by _them_ \- was a pleasure for her eyes alone.

“Hnn.” He could feel her leaking, fingers a soft slide across the semen- and lube-slicked skin of her ass. As soon as he found time to do the lab work, they’d have the chance to try that again without worry for potential offspring. Definitely had to fit it into his schedule.

“Y’know, your fangirls would never believe their smart and gentlemanly Okumura-kun to be the dirty, dirty pervert that you are.”

A soft chuckle escaped him. “Is that a problem?”

“Only in that it means they’ll keep flocking toward you like- I dunno. Birds or bugs or something else equally annoying.”

In one quick movement, Rin was pinned down on her back beneath Yukio’s looming form. “And what if,” he murmured against one sensitive ear, “that brought them out in droves?”

Rin ignored the challenge in his words. “Hey, wait- Don’t tell me you’re ready to go again, already?”

“Hm? Maybe~” Teeth latched onto the pointed tip of an ear, gnawed lightly in the way she enjoyed most. Rin’s mewl of pleasure and strong legs that pulled him closer made him nearly purr in satisfaction. But… “No.”

“Eh?” Rin blink-blinked, confused.

“Sleepy now. Be my pillow.” Yukio nuzzled into her chest with a yawn.

“Hey, wait- Oi! Yukio, you stupidly heavy bastard…”

Yukio tuned her complaints out the same way he had numerous times over the years in favor of falling into a light doze.

  


* * *

  


In their own ways both Yukio and Rin had always been possessive of one another. It had never amounted to much by the time they were teenagers as Rin, despite her pretty face and curvy body, was feared for her physical strength and temper while Yukio was too busy playing oblivious so as to keep the peace between his not-so-small army of fangirls.

Once Rin had begun to train as an exorcist, though… Everything changed.

  


* * *

  


Renzou didn’t know what he’d done to get so lucky, but if he could he would do it all over again.

The beach! (For a mission.)

With Izumo-chan and Rin-chan! ( _Okumura-chan_ , he had to remember. The look on Okumura-sensei’s face when Renzou had become overly familiar with his sister was seriously frightening. And he had grown up around the Houjou sisters.)

Still, the sun and sea and pretty girls in their swimsuits~ There was no better place to be~

  


Scratch that. Crappy mission is _seriously_ crappy mission. And for all the enjoyment during his off time, it seemed as though the prettiest ladies were always out and about whenever he was overheating at the ikayaki stand.

Although Rin-chan (Okumura!) was quite the beauty herself in her chosen outfit. Long, dark hair pulled up in twin tails - girlish as she so rarely appeared - that brushed her bare shoulders. Bare, bare shoulders. Two sets of straps, soft yellow and bold red, tied in easy knots, neck and back both.

Renzou had never seen so much of her skin before. Who knew that the school’s uniform blouse hid so much of her~ Although the long shorts, a plain blue denim that covered more than her uniform skirt rather than matching bikini bottoms left something to be desired. Even so, the lack of Rin-chan’s usual tomboyish appearance was worth celebrating.

Plus, Izumo-chan with her bikini and hair tied up in a high tail that bared the long lines of her neck. Renzou was so lucky~

  


“Oi, Shima.” Rin tapped one foot as she waited for him to catch up. Now that the mission was over, no way would she let him “miss” the bus just to get a bit more time at the beach. (She _lived_ with Yukio, who bitched about things often enough. Like she _wanted_ to add to that?)

“Hm? Yes, R- er, Okumura-chan?” Renzou tried to ignore the way Rin-chan’s arms crossed beneath her breasts so as to emphasize them even in the loose top she wore. Now that he _knew_ …

“I’ll make you a deal, Shima.” The cutesy tilt of Rin’s head and toothy little smirk should have been warning enough. That she readjusted her arms and knew just what that did to her chest, well. Weapons of war, naturally.

“Oh?” Nice view~

“Delete every picture you took that has me in it. From your phone, your camera; whatever.”

“Eh?!” Shit shit _shit_ , how did she even _know_ that?

“ _Delete_ them. And I’ll forget not only the flirting and ogling, I’ll forget you calling me ‘Rin-chan’.”

“Ack.”

“I didn’t know you objected to being called by your name,” Izumo frowned. What did she have to trade to delete the pictures of herself? “Moriyama does it.” Outright threats toward him, maybe? Nothing that would get her in trouble at school, though…

“I don’t. Yukio takes offense. But he’s known Shiemi a long time, so…”

“Ah, right.” Izumo didn’t have an obsessive brother to wield like Okumura, so that was out. Paku? She’d definitely give Shima a stern talking to, but that’d just put her into the perverts target range again. _No._

Renzou paled. He hadn’t thought there’d been many slips with the name thing. Between that and the pictures, he was _so dead_. Okumura-sensei was possessive and protective of his sister to a disturbing degree. Not that it was _any_ of Renzou’s business. Or that he would ever judge. Or do anything untoward to Okumura-chan, _ever_. (Again. Ever _again_.)

“Ahahaha, why don’t I just-” Fingers flew, deleted pictures and video alike; anything with Okumura-chan in it. “There. All done.”

“Good.”

Rin’s smile, amused and devious, was dazzling. It was only fitting, Renzou supposed, that such a pretty and friendly - if not necessarily nice - girl had a brother who was scary enough to get even Renzou to stop flirting. (Or try to. He had only so much control, after all. His brothers were probably right that it would get him killed violently one day.)

Maybe the next beachside mission they had, he’d be assigned to work with Izumo-chan and Moriyama-san. That would be nice~

  


* * *

  


Shiemi had even more curves than Rin (softer, less athletic and tomboyish), especially noticeable once she’d finally ditched the kimono for more practical mission clothes. She was also genuinely nice and _polite_ , something Rin hardly ever made an effort to be. In most ways, she generally appeared to be a pretty damn perfect match for _Yuki-chan_.

A part of Rin kind of wanted to hate her, but Shiemi didn’t deserve that at all. And Rin actually _did_ like her, sweet and stubborn and innocent as Shiemi was.

So Rin didn’t have a clue as to just _what_ was wrong with herself. Sure, she was still adjusting to some of the changes in her body and mind due to the unsealing of her powers. But why she couldn’t fight the urge to snip and snarl at Shiemi - her first real friend, Yukio not to be counted for obvious reasons - at random moments, Rin just couldn’t explain. The sheltered young woman would likely never be able to make sense of the mixed signals she was being sent, to Rin’s mixed dismay and thankfulness.

Neither did Rin understand her need to check Yukio’s scent at every opportunity, to make sure her own was the predominant of all other scents upon him aside from Yukio’s own. Or why she liked to have his scent upon herself- Quickies in a classroom, an abandoned corridor; with minimal cleanup leaving them both a bit sloppy, covered in one another and _just right_ to her senses.

But those things allowed Rin to go back to Shiemi’s side with a smile, not sharp eyes that had even Kamiki noticeably glancing at Rin strangely.

(Though if things continued in the direction they were headed libido-wise, one of them was going to end up so tired of sex as to declare _celibacy_. And with Rin’s luck, it would not be her to do so, no matter that Yukio was still a healthy teenage male.)

  


More and more often, Nee-san had accused him of hiding himself away from her emotionally. Which wasn’t precisely a wrong statement. Even before, years before, he had been; but ever since Tou-san…

That wasn’t the issue, though, not really. Yukio had been reminded, in those times of nearly losing the last member of his family, that it was not a tie he wished to see broken. They were working their issues out, together, and- It’d be fine. Things like that simply took time.

Yukio just wasn’t used to others having claim over Nee-san’s time or attention outside of a fight or the church. And it wasn’t Suguro-kun’s fault that he was the epitome of everything Nee-san had ever said a man should be, growing up. Yukio just- It was still a period of adjustment and-

He really couldn’t stand that Nee-san had accepted Suguro-kun’s blushingly-given peace offering. Rin had a million and one different hair decorations thanks to Tou-san’s desire to see her appear more cute and lady-like; couldn’t she manage to keep one on hand when necessary?

(And that had been before Pheles-kyo continued the tradition in Tou-san’s absence.

For all their apparent differences, Tou-san and Pheles-kyo were much more alike than most realized. Tou-san’s actions had, at turns, amused and annoyed Yukio. Mephisto Pheles left Yukio with gritted teeth as Rin gave her confusedly blushing thanks to the demon.

Her reaction was probably more due to reminding Nee-san of Tou-san than of actual appreciation, but Yukio had been wrong before in figuring out the differences in accessories that Rin adored and that Rin hated.)

  


* * *

  


“Oi, you. Ahh…Sssuguro-kun.”

“Okumura-sensei?”

Ryuuji tried not to cringe at the dark expression on Yukio’s face. Though the man held his liquor better than his twin sister, that apparently did not make him any easier to deal with when intoxicated. How had Ryuuji managed to be the only sober one amongst the group? He was pretty sure it was Shura-sensei’s fault, but it was hard to remember the exact blur of words and already half-drunken laughter. (Being sprawled out in one of the old dorm’s lounges meant they didn’t _need_ a designated driver, had Ryuuji even been able to legally drive. Which he _couldn’t_.)

Even _Moriyama-san_ was flushed pink as she clung to a creepily giggling Kamiki. So unfair…

Yukio grabbed Rin from where she lounged against Suguro’s arm. A drink-sloppy smile bloomed at the sight of her precious younger brother’s face. She snuggled herself into his side; arms wound around Yukio’s torso, Rin hummed happily.

“Yukioooo…”

Ryuuji was just glad to stop the drunken drooling on his shirtsleeves. He’d have pushed her away, but she was a _girl_. Even if she was an annoying one with demonic strength he still tried to be careful with women. (Sure, in the beginning he had been kind of an ass, but Okumura had registered more as a guy to Ryuuji’s senses, despite the blatantly obvious feminine curves. Kamiki…was Kamiki. She didn’t count.)

“Sstay away from my Nee-san, Ssuguro.” Yukio wrapped himself around Rin in response, tugged her in between his legs to nuzzle against his chest. “Unless you wanna hurt. A lot. An’ wish you were dead. A lot. ’Cause I know how t’do that. An’ no one’ll ever know. _Ever._ ”

“Whatever you say, Sensei.” Ryuuji had no desire to even lightly touch that landmine, not for anything in this life or beyond.

Neither appeared openly excessive about it, but both Okumura siblings were quite a bit overprotective of the other. Seeing them as they were currently, so tightly wound around one another, and being able to easily piece together conversations past… Well. At the best of times, people didn’t like to be accused of having a sister- or brother-complex. Especially if they did. And what was between the Okumura twins was well beyond anything so simple as that.

He made a mental note to remind Shima to _never again_ flirt with Okumura, especially in front of Okumura-sensei; no matter that his friend had mostly backed off after that one beachside mission with Okumura and Kamiki. The last thing Ryuuji needed was to have to explain to the Shima family why their youngest son had been sent back to them in bullet-ridden pieces. If there remained anything left _to_ send back at all. Drunk or not, Okumura-sensei hadn’t been lying about his abilities; not even Ryuuji had that kind of genius and doctors - Exorcists or not - could be fucking scary.

Even with his shitty alcohol tolerance and having been forbidden from imbibing, there was not enough alcohol in the _universe_ for this, seriously.

  


* * *

  


**part three - fall apart, together**

  


Yukio had his part to play in the plans to come. His newly instated rank of Paladin was not just for show.

Maybe no one would understand. Maybe they would hate him. That was fine, if it meant Yukio had the power needed to save himself and Nee-san.

Hope was the most dangerous weapon a person could wield.

(And if Yukio truly had wanted to shoot the gun aimed at Kuro, he would keep that unsightly rage to himself. He remembered the days Rin would cradle the familiar close, flopped down on her bed. The cutesy baby-talk she would never admit to as Kuro rub-rub-purred against her chest.

Yukio had hated it then, but Kuro’s importance to both Tou-san and Nee-san had forced him to ignore the feeling.

He didn’t have to ignore it any long.)

  


* * *

  


He was a moron.

Few people other than Nee-san and Shura-san had ever referred to Yukio as such, but as they knew him better than anyone else; knew him better than he knew himself-

Yukio’s stupidity knew no bounds.

Nee-san was screaming, bloody and in agony as she was used to open the Gehenna Gate. Healed rapidly only to bleed more and more.

This was what Yukio’s desperation had led to. What his stubborn refusal to let go of a lifetime’s resentment had brought about. Tou-san would be shamed by Yukio and his actions. Yukio shamed himself.

But… Maybe he could still fix things. Even if he couldn’t stop the plan that had been put in motion, Yukio could still save Nee-san from being a living sacrifice for the Pope’s madness.

“Then… Use me instead!”

Rin was curled up on her side as though she were asleep, Kurikara placed next to her, and Yukio had never hated himself more.

A sharp slice from his claws got the blood flowing. His glasses shattered-

And everything exploded in a scream of blue.

  


“Yukio… Is that Yukio?”

_No._

No, no. Not again. It couldn’t possibly be happening again. Not in such a way.

Not to _Satan_.

But that laugh. God, she would never forget that laugh. Rin still heard it in her nightmares. Felt the power of those blue flames and could taste the sharp tang of blood in the air. Saw her father drive that pendant through his own heart to stop the being that possessed him from taking her.

Satan couldn’t, _wouldn’t_ , steal Yukio from her, as well. Rin could not lose him, the other half of her.

She _refused_.

“Get out of Yukio’s body!”

  


They had been so close, hands clasped together.

And then-

He had shot her. Had shot the one person in the world who had always meant more to Yukio than anyone else, including himself. In all of the ways, big and small, that Yukio had betrayed Rin, it was the worst.

(Beating her was one thing; Nee-san had been an _idiot_ for trying to save him that way. But her screams had woken him up so- so-)

_Help me, Nee-san…_

Even if Yukio wasn’t in full control of his body, even if it was _Satan_ who possessed him-

It was still his own finger that pulled the trigger.

Yukio had turned his weapon on his sister. Had done more than just threaten her. Had not merely waged war as someone else’s puppet in the hope of them regaining their humanity.

_How? How could you do this? Make **me** do this? To **her**!_

Never again. Yukio would never again be used as a weapon against Nee-san. No matter what he had to do to stop it.

_Is this what you felt back then, Tou-san? Why you did what you did? I think I finally understand. And I’m so sorry I ever blamed Nee-san._

Okumura Yukio had learned many things from the man who had been both father and teacher to him. In so many ways, his path had followed in the shadows and footsteps of Fujimoto Shirou’s own. This was just one more lesson he had learned.

So he turned the gun on himself.

“We’re the only ones who will die here!”

  


Yukio was a fucking _idiot_.

“What the hell’s up with that cool act all by yourself?”

And Rin- Rin had had enough.

“Would you be all right with defeating Satan by killing yourself? Like hell I’d let you!”

Tears, the kind of tears she hadn’t shed since the last time Satan had stood before her wearing the body of a man she loved.

“Don’t you understand how the people left behind feel?! I don’t want to feel like that again!”

“Nee-san…”

Yukio could feel the warmth of his own tears, even over the heat of those blue flames, as he cried before his sister for the first time in years. As he willingly showed her his weakness in a way Yukio had forgotten how to do.

And the blue flames faded away.

“I’m so sorry, Nee-san, sorry…”

Rin pulled him against close, Yukio sobbing into her shoulder. Finally, after so many years, the walls between them had been torn down.

  


* * *

  


**epilogue: one and one, the sum**

  


Night had passed, and the sun shone once more on True Cross Academy. Those who needed treatment had been seen to medically, civilians in panicked aftermath dealt with, and certain members of the Order were finally allowed the rest they needed after such drama and trauma.

Yukio and Rin had yet to leave the room they’d barricaded themselves in after Shiemi ultimately reassured herself of their overall physical conditions and let them go. No matter how powerful or fast-healing the two were, the gentle Shiemi had been worried enough to actually _yell_ at the both of them before pulling the siblings into a tearful, relieved embrace.

When they had finally separated from friends all in varied stages of exhaustion, both twins stripped themselves of their bloody, torn clothes to settle in for the night - day, whatever - determined to not leave it for a _week_. Maybe longer. Not for food, nor drink, not even the baths they both so desperately needed after the arduous battle they had fought (against fucking _Satan_ and his minions, no less).

Neither were they resting in that warm, dimly lit room. Not yet. Not when they’d come so close to losing one another for good.

Rin nuzzled happily against Yukio’s newly-pointed ears, breathed in deep of his altered scent beneath blood, sweat, and fatigue. It wasn’t a bad change, just new and different; but it was still Yukio, so her instincts were luckily not causing Rin to lash out at him.

In truth, it was just the opposite; Yukio had known just how much damage her body could take, but Rin had always been so careful with him. Even when leaving territorial marks and bites all over Yukio’s body she’d held back in certain ways. He wasn’t weak, but Yukio had nothing near to Rin’s own strength even before the seal on her demonic powers had been broken.

(A part of Rin - the distant, rational part of her that she so often ignored in favor of action and reaction - finally relaxed, reassured by the strength of _her Yukio_.)

Yukio was the one now holding back, lest he harm Rin more than his actions had done already, indirectly or directly. But with every moment and movement, his confidence grew. He knew what Nee-san liked and wanted, knew her body and how to satisfy it better than he knew his own changed form. It wasn’t as though she wouldn’t let him know if she didn’t like what he was doing to her at any given moment.

Pinned beneath Rin’s weight, Yukio ran his hands down the bare skin of her back intently, pressed his fingers _just so_ into the skin surrounding the base of Rin’s tail to draw a long, low moan from her. All of those parts that made her, parts Yukio had once denied in some part of his mind due to the lack of humanity in them, never failed to accept his own flawed self. Demon or not, Nee-san was more human than Yukio had ever been. Nothing mattered more than the warm weight in his arms, than the sister that had always been with him. He would not screw that up, not ever again.

They’d figured out, with trial and error after the whole mess that resulted in Rin’s powers being unsealed, how best to work around and work with her newly demonic form. Once again, that knowledge and experience was being put to use with Yukio’s altered body. Ears and fangs, claws and tail; he had handled them well enough in public so far, short though that time had been, but private matters such as sex were a completely different issue.

Rin knew what worked and didn’t, especially with her tail (which was like an on switch for sex, no lie). Finally, after so much time the tables had been turned…

She flipped them over effortlessly, wrapped her arms and legs around Yukio’s bare form with a toothy smirk. Determined hands trailed easily across Yukio’s skin, a mirror to her twin’s earlier actions.

Yukio stiffened at the movement, eyes blown wide and sightless as they stared down at her. Those soft fingers down his back and _oh, God, yes_ that, that was the spot, right- right-

_There._ Rin watched, enjoying the sight of Yukio’s face twisted in a pleasure he’d never experienced before. Eased up, fingers slid softly away, she let him catch his breath before beginning once more. Then again. And again.

“Nee-san,” he panted, face buried in her shoulder. His breath tickled her skin, ignored the dark strands of hair that stuck to them both. “Nee-san… Nee-san… Please. I need- _Please._ ”

His cock pressed against her slick warmth, hard and needy and- Yeah. She could give him that, since he asked. She might tease on occasion, but Yukio was the sadist, not Rin.

“Are you ready for that? For sure?” Nails ran up and down his sides, avoided what they both wanted until she received an answer.

“Yessss.” The hiss of his words, the scrape of fangs pressed against the soft swell of her breast as he finally slid inside of her - that was all the encouragement she needed.

Yukio spread Rin’s thighs open wide, wider, her knees nearly flat on the bed to either side of her; pressed closer and deeper with each desperate movement and thrust.

A soft, eager whine escaped Rin as she scratched at the soft skin she had played with before. One set of nails dug into that delicious bundle of nerve endings as the other hand slid down to wrap her fingers around the slim breadth of Yukio’s tail. Rin touched and teased it the way she would have his cock; soft and fast, then slow and hard. Rin had lost track of her own tail, wayward as it so often was when not being given attention, until the length of it wound tight around Yukio’s own; furred tip flicking around the base of Yukio’s tail before stroking determinedly and being stroked in return.

They both let out sharp screams at that. Yukio drowned in the foreign sensation of his tail’s sensitivity, fangs biting down to break the skin he had been worshipping with lips and tongue. Rin, mindless in her pleasure, filled and touching while being touched with just that slight edge of pain at the manhandling of her body.

It was a blur after that, instinct and need and _together_ and _alive_ and _mine, mine, mine_ -

  


When Yukio came to, his body was more relaxed than he could ever remember it being. Nee-san was pressed softly into his side, face buried against his chest and mussed hair curling over the bare, warm skin of her shoulders.

They needed to clean up; needed to take proper countermeasures after their previous activities. Who knew precisely how his changed physiology would affect the contraceptives they usually counted on and neither one of them had even _thought_ of bothering with condoms or their usual standby of anal sex, as they had when Rin’s powers were unsealed. And when he allowed himself the time to fully think on that, he’d have to deal with the ensuing panic and its necessary aftermath. But at the present, Yukio was perfectly content as he was.

So he ignored the part of his mind that never seemed to shut up in favor of letting his twin’s steady breathing calm him down.

And slept.


End file.
